Water Cycle - Atmosphere (6)
Pre Lab 

   
OBJECTIVES:
  • Exploring atmospheric motion.
  • Discovering the jet stream.
VOCABULARY:
  • doldrums
  • jet stream 
  • polar easterlies
  • trade winds
  • westerly winds
MATERIALS:

Students chart wind direction on a map.

BACKGROUND:

The Earth is a rotating sphere.  The atmosphere as well as the hydrosphere (oceans and large lakes), move because of this rotation.  There is a difference between local and  general world-wide winds.  General winds include those that stretch thousands of miles over the Earth's surface with almost  permanent directional patterns.  Local winds are characteristic of particular geographical regions and exert a pronounced influence on the local climate.

The pattern of the general wind circulation is primarily determined by the unequal heating of the atmosphere at different latitudes and altitudes and by the effects of the Earth's rotation (Coriolis effect).  The general wind pattern includes doldrums, jet stream, polar easterlies, trade winds, and westerly winds. 

Doldrums refer to a quiet area where the wind doesn’t blow for long periods of time.

The  tradewinds are characterized by the steadiness of their direction and speed, especially over the oceans.  The jet stream refers to a narrow current of strong westerly winds in the upper troposphere.  The polar easterlies refers to an easterly wind belt found between the weak polar anticyclone and the westerly depression.  The trade winds are predominately easterly winds that blow steadily over the ocean areas.   The westerly winds are strong winds blowing from the west.

PROCEDURE:

  1. Use the diagram on “Atmospheric Winds,”  to help show students the different wind systems of the Earth.  Point out that the zone of the doldrums is where the pressure is lower than farther north or south.  The winds in this zone are light and irregular in direction with frequent calms.  The trade winds are characterized by the steadiness of their direction and speed, especially over the oceans.   Notice that because the jet stream is in the upper troposphere and changes direction due to changing pressure zones, students cannot draw it on the map. 
        

  2. Students should look at the map of global wind patterns.  On the blank map of the globe  have students try and simplify the diagram.  Give each zone a different color and have the students decide what the limits of an east-west direction would be for each zone. 
       

  3. Students may have heard of the jet stream, which is a very rapid wind that moves around the Earth from west to east at an altitude of 14-16 km.  You may want to illustrate the jet stream by doing the following demonstration. (Make sure you practice before doing this.)  Challenge your students to perform this task!

    Use a 12-16 cm straw.  Put one end of the piece in your mouth, tip your head back; hold a ping pong ball a few inches above the other end. Blow as hard as you can, simultaneously releasing the ball. The ball will remain suspended in mid-air. The harder you blow, the higher it "floats" above the straw. You can use a hair dryer, with more dramatic results.

    This demonstrates the jet stream, when air is in rapid motion  its pressure is lowered. The ball is actually imprisoned by the column of upward rushing air. As soon as it wobbles a bit to one side, the greater pressure outside the "jet stream" forces the ball back into it again. 
      

  4. Students can create their own jet stream by using the Bernoulli pipe.  Students do not have to put their mouth on the pipe.  They can just blow into the hole.  However, if they do blow into it, make sure you have some alcohol available so you can wipe it clean between uses.

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